Information storage devices typically include a head for reading and/or writing data onto the storage medium, such as a disk within a rigid disk drive. An actuator mechanism is used for positioning the head at specific locations or tracks in accordance with the disk drive usage. Linear and rotary actuators are known based on the manner of movement of the head. Head suspensions are provided between the actuator and the head and support the head in proper orientation relative to the disk surface.
In a rigid disk drive, head suspensions are provided which support a read/write head to "fly" over the surface of the rigid disk when it is spinning. Specifically, the head is typically located on a slider having an aerodynamic design so that the slider flies on an air bearing generated by the spinning disk. In order to establish the fly height, the head suspension is also provided with a spring force counteracting the aerodynamic lift force.
A head suspension of the type used in a rigid disk drive comprises a load beam and a flexure to which the slider is to be mounted. Load beams normally have an actuator mounting portion, a rigid section, and a spring region between the actuator mounting region and the rigid section for providing the aforementioned spring force. The flexure is provided at the distal end of the load beam to which the slider is mounted and permits pitch and roll movements of the slider to follow disk surface fluctuations. Flexures are known that are integrated into the design of the load beam and those formed as a separate element fixed to the rigid region of the load beam.
In providing the spring force to the rigid section of the load beam for counteracting the aerodynamic lift force against a slider, a preformed bend or radius is made in the spring region of the load beam. The radius provides the spring force and thus a desired gram loading to the slider for a predetermined offset height, the offset height being a measurement of the distance between the mounting height of the head suspension and the slider at "fly" height. Constraints of the drive design, including the spacing of the disks within the drive, factor into the predetermined offset height. In any case, the gram load at the offset height provides the counteracting force to the aerodynamic lift force to establish the "fly" height of the slider above a disk surface. As used hereinafter, the term "loaded" head suspension means the head suspension combined with the slider at "fly" height and in equilibrium under the influence of the aerodynamic lift force and the oppositely acting spring force.
The radius area of the spring region is not only responsible for loading, but has also been determined to have a large impact on torsional resonance characteristics of the head suspension. Resonance frequencies of the head suspension, if not controlled, can lead to off-track error within such a disk drive. Head suspensions are designed to optimize performance even at resonance frequencies, which include a lateral bending mode and torsional modes. More particularly, it is a design criteria to reduce or eliminate the movement or gain of the head at the resonance frequencies of the head suspension. The head suspension is also designed to have certain resonance frequencies higher than the vibrations experienced in the disk drive application.
Analysis has shown that the longitudinal side profile, hereinafter "profile" of the head suspension in a loaded state has a great influence on the off-track motion caused by the torsion modes. Thus, the performance of the head suspension at torsional resonance frequencies can be optimized by controlling the profile. The profile is largely controlled by the design of the radius within the spring region of the load beam. Techniques for optimizing the head suspension profile by specifically designing the spring region of a load beam are disclosed, for example, in U.S. Pat. No. 5,065,268 to Hagen and U.S. Pat. No. 5,471,734 to Hatch et al. Moreover, in order to properly design the radius area and spring region for optimal resonance performance, it is clearly recognized that the design must also account for the desired load to be generated by the spring region so as to define the appropriate "fly" height. Thus, a variation of the radius within the spring region that may be made to change a desired loading will also change the profile of the head suspension and thus its torsion resonance characteristics. Likewise, changes made to optimize torsion resonance characteristics affect the load provided by the spring region.
Head suspensions are designed and manufactured to perform with desired specifications for each particular application within a disk drive. Such specifications typically include the load necessary to establish the desired fly height combined with the performance characteristics which can further depend on disk spacing, storage densities and disk sizes. With a given load, the radius of the spring region of the head suspension is preferably also optimized for performance so as to minimize the effects of torsion resonance.
However, even with manufacturing the head suspensions with very close tolerances, other factors may affect the ultimate performance of the head suspension that depend largely on the assembly into the particular application. Handling of the head suspension after production can slightly change its characteristics. Likewise, variations, including manufacturing tolerances within the disk drive manufacture and/or assembly may affect the head suspension performance. For example, the spacing between disks may be slightly varied. Thus, factors beyond the control of the manufacture of the head suspension may necessitate minor adjustments to the head suspension after manufacture. The load may need adjusting because of spacing variations, which would be accomplished by changing the bend of the radius area of the spring region. What this also does, however, is affect resonance characteristics, particularly, the torsion resonance characteristics.
Head suspensions are also susceptible to being slightly altered in the handling and assembly of one or more such head suspensions within the disk drive. Typically, a plurality of head suspensions that have been combined with sliders are connected in a stack or E-block and comb structure for transport and connection to the actuator assembly of the disk drive. In this structure, the stack of head suspensions and sliders are lifted and held in that position until the plurality of sliders, as connected with the head suspensions, are interleaved between the corresponding disk stack of a rigid disk drive. Slight plastic deformation of the head suspension may result from this backbending which can again affect the load provided by the head suspension as well as its torsion resonance characteristics. The loss in load force as referred to throughout this application is defined as "load loss." Moreover, since this load loss can occur at the final stage of assembly, performance characteristics of the head suspension(s) can be ultimately affected. That is, the load may be slightly off and the resonance performance may no longer be optimal.